1. Field
An aspect of the present invention relates to a printed wiring board having lands and an electronic apparatus equipped with it.
2. Description of the Related Art
For example, a printed wiring board is disclosed in which lands for grounding are disposed around fixing holes for bolting of the printed wiring board. This printed wiring board is equipped with a substrate, the fixing holes which penetrate through the substrate, the lands which are donut-shaped and are formed around the respective fixing holes on the surface of the substrate, and cream solder members which are printed on the surfaces of the lands.
In printed wiring boards of this type, usually, the surfaces of the lands are subjected to solder plating to prevent corrosion of the lands and attain reliable grounding. A printed wiring board having a cost advantage over ones in which the lands are subjected to solder plating is provided by supplying solder also to the land surfaces when cream solder is supplied to mounting patterns of other components (see JP-A-2000-244080, for instance).
In recent years, with the increase in miniaturization and functionality of digital equipment, the high-density mounting on a printed wiring board and the securing of a wide mounting area have come to be required increasingly. However, the above donut-shaped lands raise a problem that the mounting area on the printed wiring board is reduced by areas corresponding to the spaces for formation of the lands. For another thing, to secure a wide mounting area on a printed wiring board, it is effective to locate the fixing holes as close to the outer periphery of the board as possible. However, in the printed wiring boards, the fixing holes cannot be located sufficiently close to the outer periphery because margins for formation of the donut-shaped lands need to be secured around the respective fixing holes.
Each of these margins needs to be set taking into consideration not only the space for formation of the land but also a variation that may occur when a land pattern is formed by etching. This is because if a land is formed in contact with the periphery the land is exposed in an end face of the printed wiring board, as a result of which the printed wiring board may be short-circuited with another component. This also requires sufficient margins around the respective fixing holes.
On the other hand, one method for reducing the above margins is to narrow the widths of the donut-shaped lands. However, if the land widths are narrowed, a land pattern may be disconnected due to a variation in forming the pattern. Furthermore, since the lands are reduced in strength, the land patterns are prone to peel off when bolting is performed through the fixing holes.
For the above reasons, the printed wiring boards cannot sufficiently satisfy the recent requirements of high-density mounting and securing of a wider mounting area.